1. Field of the Invention
The present invention relates to an electromagnetically actuated fuel injector.
2. Brief Description of Related Developments
An electromagnetic fuel injector normally comprises a tubular supporting body having a central channel, which acts as a fuel conduit and terminates in an injection nozzle regulated by an injection valve controlled by an electromagnetic actuator. The injection valve has a pin connected rigidly to a movable armature of the electromagnetic actuator, and which is moved by the electromagnetic actuator between a closed position and an open position respectively closing and opening the injection nozzle in opposition to a spring which keeps the pin in the closed position.
One example of an electromagnetic fuel injector of the above type is described in U.S. Pat. No. 6,027,050-A1, which relates to a fuel injector having a pin which cooperates at one end with a valve seat, and is integral at the opposite end with a movable armature of an electromagnetic actuator; the pin is guided by the armature at the top, and at the bottom by the end portion of the pin sliding inside a guide portion of the valve seat.
Known electromagnetic fuel injectors of the above type are widely used, by combining good performance and low cost. Since injectors with an electromagnetically actuated pin, however, are unable to operate at very high fuel pressures, injectors with a hydraulically operated pin have been proposed, i.e. in which movement of the pin from the closed to the open position, in opposition to the spring, is produced by hydraulic forces. Examples of such injectors are described in Patent Applications EP-1036932-A2, EP-0921302-A2, and WO-0129395-A1.
Though of good dynamic performance and capable of operating at very high fuel pressures, injectors with a hydraulically actuated pin are complicated and expensive to produce, by requiring a hydraulic circuit with a piezoelectrically or electromagnetically actuated control valve. Moreover, there is always a certain amount of backflow of fuel, which is drained at ambient pressure, and which has the negative effects of constituting a loss of energy, and of tending to heat the fuel.
When assembled in an injection system, the injector is connected to a pressurized-fuel feed conduit. More specifically, the tubular supporting body of the injector is connected in fluidtight manner to the feed conduit to connect the central channel of the supporting body hydraulically to the feed conduit. The fluidtight connection is normally made using a connector, which provides for a conical connection with no elastic seals, i.e. an inclined surface of the supporting body is kept pressed against a corresponding inclined surface of the connector with no elastic seal in between. However, to ensure long-term sealing of such connections, even in the presence of continuous vibration (typical of an internal combustion engine), the component parts, particularly the inclined surfaces pressed against each other, call for extremely precise machining, and as such are time-consuming and expensive to produce.